Rotary regenerative heat exchanger

ABSTRACT

A rotary regenerative heat exchanger in which inlet and outlet seals defining a path for one or other of the fluids between which heat is to be exchanged enclose respective areas of inlet and outlet end faces of the matrix of the heat exchanger of different magnitude, thereby to reduce the magnitude of the resultant axial force on the matrix. In this way forces due to fluid pressure acting on opposed end faces of the matrix can be balanced thereby to reduce stress within the matrix and also to avoid wear on the seals due to an unresolved end thrust on the matrix. Additionally, the areas of the seals can be adjusted to avoid tipping of the matrix about its axis of rotation.

United States Patent Barnard et al.

[451 Mar. 21, 1972 Appl. No.: 44,259

Foreign Application Priority Data June 11, 1969 Great Britain ..29,487/69 U.S. Cl. ..l65/9, 60/3951 H Int. Cl ..F28d 19/04 Field of Search 165/9; 60/3951 H References Cited UNITED STATES PATENTS 6/1933 Miller et a1 ..210/185 X 2,337,907 12/1943 Lundstrom 165/7 2,681,209 6/1954 7 Mudersbach. .165/9 X 3,157,226 11/1964 Atwood ..165/9 3,194,301 7/1965 Kovats 165/9 X 3,202,207 8/1965 Chute 165/9 Primary Examiner-Albert W. Davis, Jr. Attorney-Mawhinney & Mawhinney [57] ABSTRACT A rotary regenerative heat exchanger in which inlet and outlet seals defining a'path for one or other of the fluids between which heat is to be exchanged enclose respective areas of inlet and outlet end faces of the matrix of the heat exchanger of different magnitude, thereby to reduce the magnitude of the resultant axial force on the matrix. In this way forces due tov fluid pressure acting on opposed end faces of the matrix can be balanced thereby to reduce stress within the matrix and also to avoid wear on the seals due to an unresolved end thrust on the matrix. Additionally, the areas of the seals can be adjusted to avoid tipping of the matrix about its axis of rotation.

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ATTORNEY 1 ROTARY REGENERATIVE HEAT EXCHANGER- The invention relates to a rotary regenerative heat exchanger for effecting exchange of heat between two fluids. The invention is particularly, but not exclusively, concerned with a rotary regenerative heat exchanger of the kind employed in a gas turbine engine for exchanging heat between hot gases which have been expanded through a turbine of the engine and air which has been compressed by a compressor of the engine.

One type of rotary heat exchanger that has been used in association with a gas turbine engine includes a rotary disclike matrix having seals engaging the end faces of the matrix and defining paths through the matrix for the air and hot gases. Due to fluid friction in the air and hot gases passing through the heat exchange passages or pores in the matrix, pressure drops are produced in the respective streams. Hitherto the inlet and outlet areas defining the paths through the matrix for 'the hot gases'have been substantially equal and thereforethere has been unequal fluid loading on the end faces due to the difference between the inlet and outlet gas pressures. Unequal fluid loading on the end faces of the matrix imparts an axial thrust on the matrix and could tend to tip it about its axis, thereby imparting undesirable stresses in the matrix. Where the matrix is made of a brittle material such as a ceramic or like material, such as silicon nitride, these stresses could cause damage to the matrix. Also resistance to the axial thrust on the matrix would create a wear problem due to the tendency for relative movement to occur between the matrix and its housing.

According to the invention, a rotary regenerative heat exchanger comprising a rotary matrix and seals engaging inlet and outlet faces of the matrix and defining areas of said faces through which fluids between which heat is to be exchanged are to be passed is characterized in that the inlet and outlet seals defining a path for one or other of the fluids enclose respective areas of the inlet and outlet faces of the matrix of different magnitude, thereby to reduce the magnitude of the resultant axial force on the matrix.

Preferably, the matrix is enclosed within a housing having an inlet for one of the fluids between which heat is to be exchanged, whereby the whole of the inlet and outlet faces of the matrix, except those portions thereof enclosed within fluid inlet and outlet seals, is subjected to the inlet pressure of said one fluid and the matrix is engaged by a pair of seals enclosing respectively areas of the inlet and outlet faces of the matrix and defining a flow path through the housing and the matrix for said other fluid, the matrix surface area enclosed within the outlet seal being smaller than that enclosed within the inlet seal and the surface area surrounding the area enclosed by the outlet seal being greater than that surrounding the area enclosed by the inlet seal, whereby the resultant thrust on the matrix due to the inlet and outlet pressures of said other fluid and the difference in the areas enclosed by said seals is substantially balanced by an opposite resultant thrust on the matrix due to said one fluid pressure and said difference in the areas surrounding the areas enclosed by said seals.

There may be an additional seal to define the outlet area and the path through the housing of said one fluid after it has been passed through the matrix.

The said one fluid may be the cooler fluid and said other fluid the hotter fluid.

By way of example, a rotary regenerative heat exchanger, in accordance with the invention, for a gas turbine engine is now described with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic axial section through the matrix of the heat exchanger and its associated seals and indicating pressures acting on different portions of the end facesof the matrix;

FIG. 2 is a plan view of the matrix in the direction of arrow II in FIG. 1;

FIG. 3 is an underplan view of the matrix in the direction of arrow III in FIG. 1, and

FIGS. 4 and 5 are respectively axial sections through the matrix and its associated seals and housing to the left and to the right of the axis of rotation of the matrix, these figures being drawn to a considerably larger scale than in FIG. 1.

Referring to the drawings and particularly to FIGS. 4 and 5, the heat exchanger comprises a housing 1 of generally circular shape in plan supporting a spindle 2 on which the matrix 3 is rotatable. The matrix is in the shape of a fiat disc and is preferably made of a ceramic or like material, such as silicon nitride. The matrix 3 has inner and outer peripheral portions 4, 5 which are non-porous and an intermediate annular portion 6 formed with heat exchange passages or pores extending substantially parallel with the axis of the matrix. The matrix is rotated bymeans of a pinion not shown engaging a toothed annulus 7 through a radially resilient driving member 8 permitting relative radial expansion and contraction between the annulus 7 and the matrix 3. The annulus 7 may be constructed in accordance with copending patent application No. 851,704, now abandoned and the driving member 8 may be of any convenient form, for example, it may be a spirally wound spring strip or a corrugated spring strip.

The housing supports three generally sector-shaped bellows seals 9, 10, 11 (see FIGS. 2 and 3) which carry flat sealing strips 12, 13, 14 of similar shape. The sealing strips make slid ing sealing engagement with end faces 15 and 18 of the matrix. The seal 9 encloses a region 16 within the housing and a corresponding area of the end face 15 communicating with atmosphere. The seal 10 encloses a region 17 within the housing and a corresponding area of the end face 18 of the matrix. The region 17 communicates with the outlet end of a turbine of the gas turbine engine. The seal 11 encloses a region 19 within the housing and a corresponding area of the end face 18 of the matrix. The region 19 leads to a combustion chamber of the engine. The remaining portions of the end faces 15 and 18 of the matrix communicate with an internal region 20 of the housing which receives compressed air delivered by a compressor of the engine. Compressed air is therefore delivered into region 20 and hot gases from the turbine are delivered into the region 17. As the matrix rotates, air passes through heat-exchange passages or pores in the part of the matrix portion 6 shown in FIG. 5 and enters the region 19. Simultaneously hot gases pass through heat-exchange passages or pores in the part of the matrix portion 6 shown in FIG. 4 and enter the region 16. In this way, the matrix is heated by the hot gases and imparts heat to the compressed air.

Referring to FIG. 1, at the left-hand side of the housing, the pressure of gases P17 delivered by the turbine, i.e., the pressure at the region 17 embraced by the seal 10, will be greater than atmospheric pressure P16 at the region 16 embraced by the seal 9. Therefore where the seals 9 and 10 and their sealing strips 12, 13 are of equal shape and size as in known rotary regenerative heat exchangers, there would be a downward thrust on the matrix. Furthermore the compressor delivery pressure P20 in the region 20 acting upwardly from underneath the right-hand side of the matrix being higher than the pressure P19 in the region 19 enclosed by the seal 11 would tend to cause tipping of the matrix about the spindle 2.

The dominant loading is the former and the purpose of this in vention is to minimize the risk of wear or damage to the matrix. Where the matrix is made of a ceramic or like material such as silicon nitride this is of significant importance.

In accordance with the invention, the area enclosed by the sealing strip 13 of the seal 10 and subjected to the pressure P17 of gas delivered by the turbine is made larger than that enclosed by the sealing strip 12 of the seal 9. Also, the effective area of the upper end face 18 of the matrix outside the seal 13 subjected to the compressed air inlet pressure P20 within the interior of the housing 1 is made smaller than that of the corresponding part of the lower end face 15. This is accomplished by making the sector radius of the seal 10 longer than that of the seal 9 and thereby moving the peripheral portions of the bellows of the seal 10 and the sealing strip 13 closer to the outside diameter of the matrix disc. This is shown by comparing FIGS. 2 and 3 in which the sector radius of the seal is R calculated hereinafter. The pressure P17 of the hot gases in the region 17 is greater than the pressure P16 in the region 16 and as the area enclosed by the seal 10 is greater than that enclosed by the seal 9, there is a resultant downward force due to the hot gases in the regions 17 and 16 acting on the matrix. There is also a resultant upward force acting on the matrix due to the compressed air pressure P20 within the housing acting on the whole of the matrix end faces except those within the sealing strips l2, l3 and 14. By selecting appropriate dimensions of the sealing strips 12 and 13, the resultant upward force due to the compressed air can be made to substantially balance the resultant downward force due to the hot gases in the regions 17 and 16, thereby reducing stress within the matrix and also avoiding wear on the seals due to an unresolved end thrust on the matrix. Furthermore by selecting appropriate dimensions for the sealing strips, tipping of the matrix about the shaft 2 can be avoided.

A numerical example giving the difference in radius X between the seals 10 and 9 for vertical equilibrium of the lefthand side of the axis of rotation now follows. The pressure difference between the regions 17 and'l6 is 0.4 lb. per square inch and the appropriate area of seal 10 is 2 square feet. Therefore the downward thrust acting on the matrix 2X 144 X -4 1 lb. The peripheral length of the seal 10 is 52 inches and the pressure in the region is 45 lb. per square inch. Therefore for vertical equilibrium the downward resultant force derived from the different pressures P17 and P16 and the difference in areas of seals 10 and 9 must be equal to the resultant upward force due to the pressure P20 acting outside the seals 10 and 9 and thus the area difference between the seals 9 and 10 is 115/45 2.6 square inches. Therefore the radius difference, X= 2.6/52 0.05 inches.

The foregoing description refers to a matrix having a nonporous rim portion 4 and a non-porous hub portion 5. Where the porous portion of the matrix extends to the periphery of the matrix, passages or pores of the matrix that are not open at both ends to the gas path, open at both ends to the air path or sealed at both ends by the sealing strips 12 and 13 must be blocked to prevent leakage of gas through the matrix. Alternatively, the passages could be inclined to the axial direction in such a way that they will be open at both ends to the gas path,

open at both ends to the air path or sealed at both ends. by the sealing strips 12 and 13.

What we claim as our invention and desire to secure by Letters Patent of the United States is:

1. An axial flow rotary regenerative heat exchanger comprising a rotary matrix in which heat exchange is effected between two fluids passed in counterflow between spaced end faces of the matrix, a spindle by which the matrix is supported and on which it is rotatable, means for rotating the matrix about said spindle, a pair of seals respectively engaging said spaced faces and respectively enclosing areas of said spaced faces and defining a flow path through the matrix for one of said fluids, a further seal engaging one of said faces and enclosing an outlet area for the other of said fluids, said other fluids being admitted to the matrix through the other of said spaced faces externally of the seal of said pair of seals engaging said other face and a housing containing said matrix and said seals and supporting said spindle, the housing having ports communicating directly with the seals and also having an inlet port therein for the other of said fluids and communicating through the interior of said housing with both said spaced faces of the matrix externally of said seals, the matrix surface area enclosed within the outlet seal of said pair being smaller than that enclosed within the inlet seal of said pair and the matrix surface area surrounding the area enclosed by said outlet seal plus the matrix surface area enclosed within said further seal being greater than that surrounding the area enclosed by said inlet seal, whereby the resultant thrust on the matrix due to the inlet and outlet pressures of said one fluid and the difference in areas enclosed by said inlet and outlet seals is substantially balanced by an opposite resultant thrust on the matrix due to said other fluid pressure and said difference in areas surrounding the areas enclosed by said inlet and outlet seals.

2. A heat exchanger as claimed in claim 1 in which the seals are of sector shape and the inlet seal for said one fluid encloses a larger area than the outlet seal for said one fluid by said inlet sealing having its circumferential portion of larger radius than the circumferential portion of said outlet seal.

3. A heat exchanger as claimed in claim 1 in which said other fluid is the cooler fluid and said one fluid is the hotter fluid. 

1. An axial flow rotary regenerative heat exchanger comprising a rotary matrix in which heat exchange is effected between two fluids passed in counterflow between spaced end faces of the matrix, a spindle by which the matrix is supported and on which it is rotatable, means for rotating the matrix about said spindle, a pair of seals respectively engaging said spaced faces and respectively enclosing areas of said spaced faces and defining a flow path through the matrix for one of said fluids, a further seal engaging one of said faces and enclosing an outlet area for the other of said fluids, said other fluids being admitted to the matrix through the other of said spaced faces externally of the seal of said pair of seals engaging said other face and a housing containing said matrix and said seals and supporting said spindle, the housing having ports communicating directly with the seals and also having an inlet port therein for the other of said fluids and communicating through the interior of said housing with both said spaced faces of the matrix externally of said seals, the matrix surface area enclosed within the outlet seal of said pair being smaller than that enclosed within the inlet seal of said pair and the matrix surface area surrounding the area enclosed by said outlet seal plus the matrix surface area enclosed within said further seal being greater than that surrounding the area enclosed by said inlet seal, whereby the resultant thrust on the matrix due to the inlet and outlet pressures of said one fluid and the difference in areas enclosed by said inlet and outlet seals is substantially balanced by an opposite resultant thrust on the matrix due to said other fluid pressure and said difference in areas surrounding the areas enclosed by said inlet and outlet seals.
 2. A heat exchanger as claimed in claim 1 in which the seals are of sector shape and the inlet seal for said one fluid encloses a larger area than the outlet seal for said one fluid by said inlet sealing having its circumferential portion of larger radius than the circumferential portion of said outlet seal.
 3. A heat exchanger as claimed in claim 1 in which said other fluid is the cooler fluid and said one fluid is the hotter fluid. 